Refrigerating Machine Oil
Heretofore known as refrigerating machine oils are mineral oils such as paraffinic oils, naphthenic oils and the like and synthetic oils such as alkylbenzene oils, ester oils and the like. These oils are used chiefly for refrigerating machines which employ trichlorofluoromethane (R-11), dichlorodifluoromethane (R-12) or the like as a refrigerant. In recent years, however, it has been suggested that chlorine-containing fully halogenated hydrocarbons such as R-11 or R-12 released into the atmosphere would deplete the stratospheric ozone layer, thereby inflicting a serious adverse influence on the ecosystem including humans on earth. Consequently an international agreement calls for the restriction of consumption and production of specific flons such as R-11 and R-12.
It has been proposed to use CH.sub.2 FCF.sub.3 (R-134a) or like hydrogen-containing fluorinated hydrocarbons as a refrigerant substituting for R-11 or R-12. The proposed hydrocarbons are unlikely to deplete the ozone layer but poorly compatible with conventional refrigerator oils. Because of this defect, when the hydrogen-containing fluorinated hydrocarbon is used as a refrigerant in a refrigerator together with a conventional refrigerator oil, the refrigerator is made inoperative in a short time due to the lowered durability of a compressor, and the refrigerator capacity and coefficient of performance are significantly decreased.
In view of said problem, fluorine-containing oils may be used as a refrigerator oil since the oils are considered highly compatible with hydrogen-containing fluorinated hydrocarbons. These compounds are commercially available under the trade names "Fomblin" (product of Montefluos Co., Ltd.), "Krytox" (product of E.I. du Pont de Nemours & Co., Inc.), "Demnam" (product of Daikin Industries Ltd.), etc. The compounds have repeating units of the following formulas as the main structure ##STR1## wherein n and m are each an integer of 1 or more.
However, these known fluorine-containing oils are not necessarily fully compatible with refrigerants. This is presumably because these fluorine-containing oils contain little or no hydrogen in the structure. Further it is difficult to use these fluorine-containing oils for commercial purposes since the monomers corresponding to said repeating units in the structure are expensive.
When said hydrogen-containing fluorinated hydrocarbon is used as a refrigerant, fluorine- and hydrogen-containing oils are effectively used as a refrigerator oil in order to improve the compatibility between the refrigerant and refrigerator oil. Consequently the development of an expedient process for producing the fluorine- and hydrogen-containing oil is thought important to realize their use.
Fluorine- and hydrogen-containing oils are disclosed in Japanese Unexamined Patent Publications No. 205491/1991 and No. 7798/1991, etc. The disclosed oils, however, have drawbacks. For example, the oils contain, as the basic unit, a compound having a perfluoropolyether bond and the monomer used as the starting material is expensive. Moreover, because the fluorine-containing moiety of the monomer is basically COF-terminated, the reaction product of the monomer with a hydrocarbon compound is an ester and susceptible to hydrolysis. On the other hand, when a compound other than an ester is prepared, it is necessary to transform the end group --COF of the fluorine-containing compound to --CH.sub.2 OH, for example, by reduction reaction. Consequently, the reaction requires a multi-step procedure. Since the refrigerator oil thus prepared is expensive, it may be difficult to realize the commercial use of the refrigerator oil. The polyester-based compounds disclosed in Japanese Unexamined Patent Publications No. 128991/1991 and No. 179091/1991, etc. are reportedly highly compatible with R-134a, but are significantly hygroscopic and prone to hydrolysis or like decomposition because of the ester group present in the compound, posing a problem of durability.
Lubricant for Magnetic Recording Media
To improve the travelling stability and the durability of magnetic recording media, a method has been proposed which is to incorporate a lubricant into a magnetic layer or to coat a thin magnetic layer with a lubricant by coating methods such as dipping or spin coating. For example, the fluorine-containing polyether and the like described in Japanese Unexamined Patent Publication No. 113130/1986 are known as such lubricant.
In preparing a coating composition using said fluorine-containing polyether, the polyether is not fully dispersed in a common hydrocarbon-based organic solvent. Consequently the lubricant is readily removed from the coated magnetic layer by sliding contact of the recording media with the magnetic head, thereby making the magnetic recording media unsatisfactory in the abrasion resistance and durability.
Some fluorine-containing solvents are capable of fully dissolving fluorine-containing polyethers. Yet common solvents such as trichlorotrifluoroethane can no longer be used because of the recent problem of ozone layer depletion. Other fluorine-containing solvents (such as C.sub.6 F.sub.14) considered free of ozone layer depletion problem are expensive although able to dissolve conventional fluorine-containing polyethers. Further these solvents reportedly contribute to global warming and thus their use requires great care.